1. Field of the Invention
The present invention relates to a laser apparatus, and more particularly, to a single pulse laser apparatus capable of synchronizing a mode-locked signal with a Q-switched signal.
2. Discussion of Related Art
Recently, a treatment technique using a laser is widely being used, and a treatment apparatus using such a laser is being used in dermatology, ophthalmology, dentistry, surgery, and the like. A laser treatment apparatus used in the dermatology among these departments is generally used for treatment of lesions such as skin diseases which occurs in skin, or vascular diseases, and achieves a purpose of the treatment by irradiating the skin with a laser having a constant wavelength and intensity. Various types of lasers are used for the treatment in the dermatology. An alexandrite laser, which operates at 755 nm and is developed in 2012, is mainly used for treatment of dermatopathological pigmentation that occurs naturally, and tattoos, and uses picosecond pulses in order to maximize therapeutic effects while minimizing aftereffects. Further, a long pulsed ruby laser is used for hair removal. A neodymium-doped yttrium aluminum garnet (Nd:YAG) laser which operates at 1060 nm and a carbon dioxide (CO2) laser which operates at 10.6 micrometer, and an argon laser which operates in a range of 488 nm to 514 nm are used for treatment of ectatic vessels.
Specifically, in the dermatology, the laser treatment apparatus is used to treat various dermatopathological diseases such as stain spots, other ectatic vascular diseases, and pigmentation diseases including tattoos. The laser treatment apparatus may allow localized heating so as to increase a temperature so that constituent proteins are denatured or pigment particles are dispersed. In this case, a pulse width and energy of laser irradiating light which is appropriate for treatment of skin wounds are important in medical lasers unlike in other research and industrial lasers. Specifically, energy should be focused on an output pulse as much as possible in order to maximize therapeutic effects, and to this end, a laser capable of outputting a single pulse is required.
In a conventional technique, a pulse picker method and a cavity dumping method are used to output a single picosecond pulse and high energy. However, when these methods are used, since high-speed high-voltage circuits are required, a burden of circuit designing and manufacturing costs and power consumption occurs, since output energy is small, there is a problem in that an amplifier should be used, and a system volume according to use of the amplifier increases and a burden of power consumption and costs caused by a high voltage supplied to the amplifier occurs.
In U.S. Pat. No. 7,929,579, a method of outputting a high energy single pulse by using only a single electro-optic modulator (EOM) and a cavity dumping method is disclosed. However, in this case, since a high-voltage EOM should be used, a burden of costs and power consumption resulting from a high-speed high-voltage driving circuit occurs, and both of mode-locking and Q-switching should be performed by using only a single EOM, there is a problem in that a burden of power consumption caused by a high voltage occurs. Further, high-speed high-voltage switching circuits should be manufactured to perform both of the mode-locking and the Q-switching using a high-voltage EOM. In addition, since a high energy picosecond single pulse may be output, there is no need to use an amplifier, but since the mode-locking is not completely implemented, there is a limit to make one shot pulse.